The invention relates to a method for connecting structural units and a connection arrangement of two structural units for a vehicle body.
Many variations of generic methods for connecting two structural units for a vehicle body are known. Such methods are used at different sites in motor vehicles to increase stiffness and for reducing the weight of a vehicle body, in particular in a lightweight vehicle body. For producing the connection arrangement of two structural units, in particular lightweight materials of many different designs are used, which due to a high torsional stiffness and with this very high weight-specific energy absorption, are excellently suited for absorbing crash energy in motor vehicles. As additional stiffening element a filler and/or a foamable synthetic resin is introduced into the structural units, wherein the filler or the synthetic resin connects the structural units with the adjoining components.
From DE 12 1009 049 313 B4 for example a connection arrangement of two structural units for a vehicle body is known which each have a carrier unit which is configured as hollow profile with a reinforcement element arranged in the carrier unit. The reinforcement element is connected with the corresponding carrier unit with structural foam, wherein the reinforcement elements of the two structural units are each configured with a joining section and are joined with each other via the joining section. The components, which are connected with structural foam, are permanently fixed in their position.
The object of the invention is to provide a method for connecting structural units and a connection arrangement of two structural units for a vehicle body, which enable a tension-free stiffening of a carrier unit of the vehicle with simple and cost effective means.
According to the invention, the object is solved by providing a method for connecting structural units including providing at least two structural units for a vehicle body, each of the at least two structural units comprising at least one carrier unit configured as a hollow profile, and at least one reinforcement element arranged in the carrier unit, the at least one reinforcement element being connected with the at least one carrier unit with structural foam, orienting the at least two structural units, prefixing the reinforcement elements in the carrier units; heat treating the structural units; permanently fixing the reinforcement elements by applying the structural foam and/or an adhesive; joining the at least one reinforcement element of one of the at least two structural units with the at least one reinforcement element of the other one of the at least tow structural units via a joining section provided on the respective at least one reinforcement element. The object is further solved by a connection arrangement including two structural units for a body of a vehicle, each said two structural units comprising at least one carrier unit configured as hollow profile and at least one reinforcement element arranged in the carrier unit, wherein the at least one reinforcement element is connected with the carrier unit with structural foam, wherein the two structural units are interconnected by the steps of orienting the two structural units; prefixing the reinforcement elements in the carrier units; heat treating the structural units; permanently fixing the reinforcement elements by applying the structural foam and/or an adhesive, and joining the at least one reinforcement element of one of the at least two structural units with the at least one reinforcement element of the other one of the at least tow structural units via a joining section provided on the respective at least one reinforcement element. Advantageous embodiments and refinements of the invention are set forth in the dependent claims.
In order to provide a method for connecting structural units and a connection arrangement of two structural units for a vehicle body, which enables a tension free stiffening of a carrier unit of the vehicle with simple and cost effective means, it is proposed according to the invention that the structural units to be interconnected are oriented and the reinforcement elements are prefixed in the carrier units prior to a heat treatment of the structural units and after the heat treatment are permanently fixed by foaming and/or gluing. Advantageously the method according to the invention makes it possible that the structural units to be interconnected and the reinforcement elements are exactly oriented relative to each other in the carrier units after their mounting, and are fastened or permanently fixed in their oriented position after a heat treatment. This achieves that the carrier units are fastened or permanently fixed in an optimal and defined position relative to each other so as to be well able to absorb and distribute the forces to be transferred. This is necessary in order to ensure the function of the structural units and to prevent a buckling of the preferably skeleton-like carrier units or the reinforcement elements. The method according to the invention allows realizing an exact orienting and a fixing of the structural units and the reinforcement elements in the carrier units, because the movements of the components relative to each other can be accounted for after a heat treatment. The secure connection according to the invention of the structural components with the carrier structure of the vehicle body can improve the stiffness of the vehicle body in a targeted manner and also withstand compressive loads which do not ideally act perpendicularly on the structural components and may thus lead to torques and compressive forces. Thus ensures a very good absorption of crash energy in vehicles. A further advantage of the method is that the structural unit according to the invention can be configured very lightweight but still torsion stiff and can absorb a large portion of the crash energy acting on the vehicle because it can have a very high specific energy-absorption capacity. By improving the stiffness of the carrier structure of the vehicle according to the invention, the demands on the material and the strength of the carrier structure can be adjusted to the respective application.
In an advantageous embodiment of the method according to the invention the prefixing can be implemented as mechanical hooking and/or chemical connection. As a result the components to be connected can advantageously be pre-mounted and fixed in a defined position. Thus a chemical agent can for example be applied over a large surface area and/or constructive mechanical fastening means can be integrated in the components to be fixed to each other. In both cases a correspondingly configured vehicle body part can be prefixed or pre-mounted fast and cost-effectively. Advantageously, such a prefixing of the components enables small relative movements in closed profiles or between two components, which movements may necessarily result from the heat treatment. Using separate mechanical fastening elements or a lightweight chemical agent only generates very small material costs and manufacturing costs while maintaining the vehicle weight.
In a further advantageous embodiment of the method according to the invention internal tensions can be lowered in the structural units. The internal tensions in the components can lead to warping during the fixing and heat treatment which may lead to dimensional inaccuracies in the vehicle body. The warping may also require reworking during the final mounting such as mounting of further components, tolerance compensation etc., which causes high costs and long mounting times. As a result of the prefixing and subsequent heat treatment for decreasing internal stresses in the components, embodiments of the method according to the invention advantageously enable a mostly tension-free assembly of the components so that reworking can be avoided. The mounting means used in the pre-mounting can avoid generating internal stresses during the mounting. Because mechanical hookings and also the chemical connection in the form of adhesives only cause minor internal tensions, the internal tensions remaining in the metallic components due to small tolerances can be effectively decreased by the heat treatment. Tension-free mounted components can have a very long service life.
In a further advantageous embodiment of the method according to the invention, the carrier units and/or the reinforcement elements of the structural units can be made from different materials and/or different material combinations. This allows advantageously a simplification of the joining technique during composite construction, in particular of structural units made of different materials and/or different material combinations, which allows designing a lightweight component in accordance with a lightweight concept with different strength properties. This allows constructively adjusting the stiffness or the specific energy-absorption capacity of the structural units in a targeted manner to a crash scenario, and also allows positively influencing the crash behavior of the carrier structure or a section of the carrier structure of the motor vehicle. A further advantage of the method according to the invention is that the use of different materials and/or different material combinations is optimally suited for complicated structural units and junction geometries thereby making it possible to stiffen the carrier structure of the motor vehicle cost effectively.
In a further advantageous embodiment of the method according to the invention, the materials and/or the material combinations have different heat expansion coefficients. The strongly differing heat expansion coefficients can lead to mechanical tensions, which advantageously can be constructively taken into account and utilized in a positive manner. The thermal properties of a component positioned between two components can for example be used in a targeted manner for positioning of the component. The fact that the temperature-dependent length change of a component during heat treatment can be compensated by adjusting the starting length, means that for example components with strongly differing heat expansion coefficients such as aluminum and fiber reinforced plastics can be joined without problems. As an alternative it is possible to join components of a structural unit that have essentially identical heat expansion coefficients but in which the thermally induced length changes act essentially in different directions as a result of constructively compensating the length change of the components compensated in order to avoid generating mechanical tensions.
In a further advantageous embodiment of the method according to the invention, the materials and/or material combinations can be made of metals and/or non-metals such as carbon fiber reinforced plastics, fiber plastic composites or aluminum. This allows advantageously generating an extremely lightweight component with different strength properties, which can thus be designed fully in accordance with a lightweight concept, wherein the structural foam can serve as barrier between the structural components with different materials and/or different material combinations. As a result contact corrosion between the components of the structural unit can advantageously be effectively avoided and a structural unit can be produced which is optimized with regard to occurring loads.
Preferably the heat treatment can be implemented as curing process of a cathodic dip-coating. This also creates particularly good conditions after the subsequent drying for the adhesion of the introduced structural foam. In particular this method allows an economic treatment of the surfaces of a large number of the structural units in the mounted state and providing them with optimal corrosion protection. The cathodic dip-coating is optimally suited for such carrier structures of the motor vehicle because they can be varnished at a temperature of about 185 C in an automated and environment-friendly manner. A further advantage of the cathodic dip-coating is the even coating of metal surfaces and hollow spaces with even layer thicknesses and good surface qualities.
In a further advantageous embodiment of the method according to the invention, at least one reinforcement element of the structural unit can have at least one reinforcement rib. This allows configuring the structural unit advantageously torsion stiff and still particularly lightweight which allows distributing and transferring compressive forces over a large surface onto adjoining component surfaces. The stiffening rib can be configured uneven or even and as a result absorb increased compressive loads particularly well. A further advantage of the invention is that the variable configuration of the geometry of the stiffening rib, in particular by a targeted and/or uneven material thickness of the stiffening rib, allows adjusting the load-bearing capacity of the structural unit and the entire energy absorption capacity. A further advantage is the large surface of the structural unit, which has the stiffening rib, which allows achieving a high torsional stiffness of the foamed structural unit after introducing the structural foam.
In a further advantageous embodiment of the method according to the invention, the reinforcement elements can be connected with the corresponding carrier unit via the structural foam and/or the adhesive in a form fitting and/or force fitting and/or materially bonding connection. As a result no elaborate mounting steps or cost-intensive joining methods are required for connecting the reinforcement elements with the corresponding carrier unit so that additional costs and mounting costs can be reduced. Thus multiple complicated components of the structural units can be connected and stiffened fast and simple and cost-effectively in hard to access regions or junctions. The purpose of the structural foam and/or the adhesive is to preferably position a reinforcement element or a structural unit in a carrier unit or to fix it in its position in order to stiffen the carrier unit. Such large-area foamed structural units or carrier structures of a motor vehicle can have a particularly high torsion stiffness with low stiffness steps and can be configured with high load-bearing capacity. The structural foam or the adhesive can have a high elastic shear modulus while having a low specific weight. In addition the structural foam can prevent an electrochemical reaction between the materials of the interconnected components, which can lead to corrosion. As a result the stiffness and the quality of the vehicle body can be effectively improved.
Further a connection arrangement of two structures for a vehicle body of a vehicle is proposed which each include at least one carrier unit which is configured as hollow profile with at least one reinforcement element arranged in the carrier unit, where the respective reinforcement element is connected with the corresponding carrier unit with construction foam, and wherein the reinforcement elements of the two structural units are each configured with a joining section and are joined to each other. The at least two structural units to be connected to each other are oriented and the reinforcement elements in the carrier units are prefixed prior to a heat treatment and after the heat treatment are permanently fixed by foaming and/or adhesive connection. This results in a cost-effective production of the components and a torsion stiff and lightweight structural unit, which advantageously can be used in different regions of the vehicle body because it can be connected with further structural units and can be produced in different sizes.
In an advantageous embodiment of the connection arrangement according to the invention, the carrier unit can be configured as partially closed hollow profile. This enables achieving a further improvement of the stiffness and the load-bearing capacity of the carrier unit according to the invention without addition of additional material. Preferably the carrier unit can beside the low weight and the high stiffness have the advantage of an improved specific energy absorption capacity. Due to the configuration according to the invention of the carrier unit the impact energy acting on the carrier unit can be absorbed in a controlled manner and in particular the energy absorption capacity of the carrier unit according to the invention can be significantly improved in a simple and cost-effective manner.
In a further advantageous embodiment of the connection arrangement according to the invention, the prefixing can be implemented by using an adhesive with high expansion on rubber basis, which is capable of withstanding the different longitudinal expansions of the materials without damage. Because it is possible to use only small amounts of the adhesive for the prefixing of the components the manufacturing method can be significantly simplified. Beside a secure connection and a precise mounting of the structural unit the mounting costs can be significantly lowered. Because for the prefixing of the structural unit and the adjoining components the adhesive is only applied over individual points or over a short distance with a small surface, a sufficiently large gap remains between the structural unit and the adjoining components so that a surface treatment or varnishing or foaming in the hollow spaces can occur in a targeted manner, which allows permanently fixing the structural unit in its position particularly easily after the heat treatment.
In a further advantageous embodiment of the connection arrangement according to the invention, a PUR-structural foam can be used as structural foam. This advantageously ensures a stable and durable connection between the structural unit and the carrier structure of the vehicle body, wherein the structural foam is not visually perceptible. In addition the structural foam can prevent ingress of humidity and effectively dampen the relative movements between the structural unit and the carrier structure of the vehicle body.